Supporting base



FIG. 1 is a front elevational of a supporting base showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof;

FIG. 7 is a top, front, right perspective view thereof; and,

FIG. 8 is a bottom, front, right perspective view thereof. 

The ornamental design for a supporting base, as shown. 